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| Age-related
changes in phosphoinositide metabolism in Galdieria sulphuraria Ingo Heilmann and Imara Perera When the thermo-acidophilic red alga Galdieria sulphuraria is grown heterotrophically in the laboratory, three stages of growth can be distinguished. A lag phase immediately after transfer is followed by logarithmic growth which ceases with depletion of the growth medium. During the third or stationary phase, the amount of PtdInsP2 in whole cells increases, starting with a minimum on day 7 and reaching a maximum on day 12. Over the same time period, PtdInsP2 in the plasma membrane decreases, indicating an independently regulated pool of PtdInsP2 in the plasma membrane. Upon hyperosmotic stimulation, transient InsP3-signals of dose-dependent intensity are generated. In cells with low plasma membrane PtdInsP2, the InsP3-signals generated after osmotic stimulation are preceded by an increase in both PIP-kinase activity and putative PIP-kinase protein. With progressing age of the cell culture, an increasing percentage of the plasma membrane PtdInsP2 is lost after stimulation, indicating a role for the plasma membrane phosphoinositide pool in osmosignaling. References: Heilmann et al., 1999; Heilmann et al., 2000; Heilmann et al., 2001 |